Sadly, these solutions fail to make Netflix streaming playable in Opera Beta 25 for Mac, for me in any case.

Silverlight is installed. Yet Netflix asks to install Silverlight whenever a title is selected in an Opera tab. No similar issue in Chrome. User-Account Switcher does not solve the issue. Nor does toggling HTML5 on/off.

It's a pity. I've been enjoying using Opera until this update. Between this issue and the repeat crashing/restarting issue I've been experiencing lately, it looks like I'm going back to Canary.